SITE INFORMATION AND CORRESPONDENCE

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-J 6 f Vogue Cleaners 1 Helen Htg�ins _ 2315 N. California St., Stockton Page 2 of 3 Using USEPA-MCL guidelines, FE implied that the area of significant impact included only monitoring wells MW-3S, MW 5S and MW-51D. Monitoring well MW-3S is consistently impacted by bent ne, TPH-g, and 1,2-DCA, and monitoring wells MW-5S and MW-51D are consistently impacted by 1,2-DCA. SJCEHD re-evaluated the impact using CAE A values and concluded that the impact to the subsurface is larger and.include MW-1, MW-2S, MW-3S, MW-3D, MW-5S and MW-5D. CAEPA-MCL concentrations were exceeded in MW-2S, MW-1, MW-21D, MW-31D by 1,2-DCA; MVV-3S, MW-5S, and MW-SD are impacted by cis-1,2-DCA; and MW-3S is impacted by vinyl chloride. Sand encountered from 40'-50' bgs in MW-1, soil-boring BH-1, and MW-3 may represent a NW-SE trending channel that could be a significant migration pathway for contaminants when site groundwater is above 50' bgs. A deeper sand with unknown vertical extent is present at 70' bgs in MW-4 and MW-3 and appears to extend to 75' bgs in MW-2, M -5, MW 4, and MW-3. A high potential for this zone to act as a contaminant migration pathway exists. FE estimated thickness of the 1,2-DCA plume a 25 feet. SJCEHD considers this most likely to be an underestimation, as the vertical extent of 1,2-DCA impacted ground water has not been demonstrated. FE estimated that contaminant concentrations are declining 6% per year and presented three plots to demonstrate the decline. SJCEHD notes that if the initial benzene concentration in MW-3S is excluded, the concentration trend will show a gradual increase of benzene over time. The reported decline is totally dependent on a single concentration that may not be representative of aquifer conditions .of the time, but was probably boosted by the disruption of soil and ground water caused during installation of the well. The same observation holds for the 1,2-DCA concentration trend; disrega d the initial concentration and the trend actually appears to be increasing. The TPH-g concentrations appear to hold steady over time within a certain range of concentrations. Only the last concentration appears to be significantly lower, and one datum point does not demonstrate a trend. The two trend lines labeled "6% per year" on the 1,2-DCA plot cannot both be 6% decline lines as they would have to be parallel if plotted on the same set of coordinate axis. FE recommended in the SCM that the. newly discovered well inside the building be properly destroyed. The construction details of this well should be ascertained (with a down-hole video survey if a well log is unavailable) and included in a work plan along with the techniques to properly destroy it. The work plan should be submitted to SJCEHD in a short and timely manner. SJCEHD is concerned that the construction o MW-1 creates the potential for the well to be capable of supporting vertical mic ration of contaminants as the well may be screened across two separate sand z nes.